Exercise PhysiologyExercise Physiology

Types of ExerciseTypes of Exercise

IsometricIsometric (static) (static) exercise exercise = constant muscle length and increased tension

Dynamic exerciseDynamic exercise = rhythmic cycles of contraction and relaxation; change in muscle length

Types of ExerciseTypes of Exercise

Anaerobic exerciseAnaerobic exercise (sprinting, weight-lifting) – short duration, great intensity (fast-twitch muscle fibers); creatine phosphate + glycogen (glucose) from muscle

WHITE MUSCLE FIBERS:WHITE MUSCLE FIBERS:- large in diameter- light in color (low

myoglobin)- surrounded by few

capillaries- relatively few mitochondria- high glycogen content

(they have a ready supply of glucose for glycolysis)o2

Types of ExerciseTypes of Exercise

Aerobic exerciseAerobic exercise (long-distance running, swimming)- prolonged but at lower intensity (slow-twitch mucle fibers) fuels stored in muscle, adipose tissue and liver

- the major fuels used vary with the intensity and duration of exercise (glucose – early, FFA – later)

RED MUSCLE FIBERSRED MUSCLE FIBERS:- red in colour (high myoglobin

content)- surrounded by many

capillaries- numerous mitochondria- low glycogen content (they

also metabolize fatty acids and proteins, which are broken down into the acetyl CoA that enters the Krebs cycle)o2

Why sprinter will never win with long-Why sprinter will never win with long-distance runner at the distance of 3000m?distance runner at the distance of 3000m?

How do muscle cells obtain the How do muscle cells obtain the energy to perform exercise?energy to perform exercise?

Exerciseintensity

ADP, Pi,creatinephosphate

in skeletal musclecells

Glycolysis Oxidative phosphorylation

• Low ATP and creatine phosphate stimulate glycolysis and oxidative phosphorylation.

• Exercise can increase rates of ATP formation and breakdown more than tenfold

Muscle metabolismMuscle metabolism

Creatine phosphate and stored ATPCreatine phosphate and stored ATP – – first few secondsfirst few seconds

GlycolysisGlycolysis – after approx. – after approx. 8-10 seconds8-10 seconds

Aerobic respirationAerobic respiration – maximum rate after – maximum rate after 2-4 min2-4 min of exercise of exercise

Repayment of oxygen debtRepayment of oxygen debt – – lactic acid converted back to pyruvic lactic acid converted back to pyruvic acid, rephosphorylation of creatine (using ATP from oxidative acid, rephosphorylation of creatine (using ATP from oxidative phosphorylation), glycogen synthesis, Ophosphorylation), glycogen synthesis, O22 re-binds to myoglobin and Hb) re-binds to myoglobin and Hb)

Energy sources during exerciseEnergy sources during exercise

ATP and CP – alactic anaerobic source

Glucose from stored glycogen in the absence of oxygen – lactic anaerobic source

Glucose, lipids, proteins in the presence of oxygen – aerobic source

Alactic anaerobic sourceAlactic anaerobic source

immediately available and can't generally be maintained more than 8-10 sATP stored in the muscle is sufficient for about 3 s of maximal effortATP and CP regeneration needs the energy from oxygen source

(for "explosive" sports:(for "explosive" sports: weightlifting, jumping, throwing, 100m running, 50m swimming)

DOHA, Qatar -- World and Olympic champion Justin Gatlin added the 100 meters world record to his list of achievements with a time of 9.76 seconds at the IAAF Super Tour meeting in Doha (2006)

Lactic anaerobic sourceLactic anaerobic source

for less than 2 min of effortrecovery time after a maximal effort is 1 to 2 hmedium effort (active recovery) better than passive recoveryrecovery: lactate used for oxidation (muscle) and gluconeogenesis in the liver

(for "short" intense sportsfor "short" intense sports:: gymnastic, 200 to 1000 m running, 100 to 300 m swimming)

Fast exhaustic exercise Fast exhaustic exercise (eg. sprint)(eg. sprint)

↑ in anaerobic glycolysis rate (role of Ca2+)In the absence of oxygen (anaerobic conditions) muscle is able to work for about 1-2 minutes because of H+ accumulation and ↓pH; Sprinter can resynthesize ATP at the maximum speed of the anaerobic pathway for less than about 60s

- Lactic acid accumulates and one of the rate-controlling enzymes of the glycolytic pathway is strongly inhibited by this acidity

Bloodlacticacid(mM)

Relative work rate (% V02 max)

Intense exerIntense exercisecise Glycolysis>aerobic metabolism Glycolysis>aerobic metabolism ↑ ↑ bblood lactate (other organs use some)lood lactate (other organs use some)

Lactate Lactate threshold; threshold; endurance endurance estimationestimation

Training reduces blood lactic acid levels at work Training reduces blood lactic acid levels at work rates between approx. 50% and 100% of VOrates between approx. 50% and 100% of VO22maxmax

Muscle fatigueMuscle fatigue

Lactic acid

↓ATP (accumulation of ADP and Pi, and reduction of creatine phosphate) ↓ Ca++ pumping and release to and from SR↓ contraction and relaxation

Ionic imbalances muscle cell is less responsive to motor neuron stimulation

Lactic acidLactic acid

↓ the rate of ATP hydrolysis,

↓ efficiency of glycolytic enzymes,

↓Ca2+ binding to troponin,

↓ interaction between actin and myosin (muscle fatigue)

during rest is converted back to pyruvic acid and oxidized by skeletal muscle, or converted into glucose (in the liver)

Aerobic sourceAerobic source

recovery time after a maximal effort is 24 to 48 hrscarbohydrates (early), lipids (later), and possibly proteinsthe chief fuel utilization gradually shifts from carbohydrate to fatthe key to this adjustment is hormonal (increase in fat-mobilizing hormones)

(for "long" sports; (for "long" sports; after 2-4min of exercise) after 2-4min of exercise)

Which of the energy sources is required Which of the energy sources is required for tennis and soccer players?for tennis and soccer players?

Why oxidation of glucose is so important Why oxidation of glucose is so important in an endurance exercise?in an endurance exercise?

The rate of FFA utilization by muscle The rate of FFA utilization by muscle is limited is limited

Oxidation of fat can only support around 60% of Oxidation of fat can only support around 60% of the maximal aerobic power outputthe maximal aerobic power outputrestricted blood flow through adipose tissueinsufficient albumin to carry FFAglucose oxidation limits muscles’ ability to oxidize lipidsperhaps the ability to run at high intensity for long periods was not important in terms of the evolution of Homo sapiens (maybe the ability to sprint, to escape from a predator was more important)?

Muscleglycogencontent(g/kg muscle)

Exhaustion

Duration of exercise (hours)

Prolonged Prolonged iintense ntense workwork ↑ glycogenolysis ↑ glycolysis glycogen depletion exercise ends

(marathon runners describe this as „hitting the wall”)”)

circulating glucose cannot be sufficient for high intensity rate of glycolysisfat can only support around 60% of maximal aerobic power output

Often the intensity of exercise performed is defined as a percentage of VO2max

50% of Vo50% of Vo2max2max – glycogen use less than 50%, FFA use predominate + small amounts of blood glucose

>50% of Vo>50% of Vo2max2max – carbohydrate use increases glycogen depletion exhaustion

70-80% of Vo70-80% of Vo2max2max – glygogen depletion after 1.5-2 hrs

90-100% of Vo90-100% of Vo2max2max – glycogen use is the highest, but depletion does not occur with exhaustion (pH and of metabolites limit performance)

Oxygen consumption during Oxygen consumption during exerciseexercise

Oxygenconsumption(liters/min)

V02 peak

Work rate (watts)

↑ ↑ exercise work exercise work ↑ O↑ O22 usage usage

Person’s max. OPerson’s max. O22 consumption (V consumption (V

O2maxO2max))

reached reached

The peak oxygen consumption is influenced by the age, sex, and training level of the person performing the exercise

The plateau in peak oxygen consumption, reached during exercise involving a sufficiently large muscle mass, represents the maximal oxygen consumption

Maximal oxygen consumption is limited by the ability to deliver O2 to skeletal muscles and muscle oxidative capacity (mucle mass and mitochondirial enzymes activity).

Oxygenconsumption(liters/min)

Work rate (watts)

V02 peak

(VO2max)

Oxygenconsumption(liters/min)

70% V02 max (trained) V02

peak

(trained)

V02 peak

(untrained)

100% V02 max

(untrained)

Work rate (watts)

The ability to deliver OThe ability to deliver O22 to muscles to muscles and and

muscle’s oxidativemuscle’s oxidative capacity limit a capacity limit a person’s Vperson’s V

O2maxO2max.. T Training raining ↑ V ↑ VO2maxO2max

175

Cardiorespiratory Cardiorespiratory enduranceendurance

the ability of the heart, lungs and blood vessels to deliver adequate amounts of oxygen to the cells to meet the demands of prolonged physical activity

the greater cardiorespiratory endurance the greater the amount of work that can be performed without undue without undue fatiguefatigue

the best indicator of the cardiorespiratory endurance is VOVO2max2max - the maximal the maximal amount of oxygen that the amount of oxygen that the human body is able to utilize human body is able to utilize per minute of strenuous per minute of strenuous physical activityphysical activity

Methods for determination of VO2maxMethods for determination of VO2max

Direct measuringDirect measuring of volume of air expired and the oxygen and carbon dioxide concentrations of inspired or expired air with computerized instruments

Submaximal tests (samples):Submaximal tests (samples): - step tests, run tests- stationary bicycle ergometer (Astrand-Ryhming test)- Physical Work Capacity (PWC 170/150) test

How does the respiratory How does the respiratory system respond to exercise?system respond to exercise?

• during dynamic exercise of increasing intensity, ventilation increases linearly over the mild to moderate range, then more rapidly in intense exercise

• the workload at which rapid ventilation occures is called the ventilatory breakpointventilatory breakpoint (together with lactate threshold)

Respiration during Respiration during exerciseexercise

Lactate acidifies the blood, driving off CO2 and increasing ventilatory rate

Major factors which stimulate increased Major factors which stimulate increased ventilation during exercise include:ventilation during exercise include:

neural input from the motor areas of the cerebral cortexproprioceptors in the muscles and joints body temperaturecirculating NE and E pH changes due to lactic acid

It appears that changes in pCOIt appears that changes in pCO22 and O and O22 do notdo not play play significant role during exercisesignificant role during exercise

Rest Exercise intensity V02max

Arterial blood

pH

Before expected exercise begins, Before expected exercise begins,

ventilation ventilation risesrises

'emotional hyperventilation‘

at any rate, impulses descending from the cerebral cortex are responsible

so do chemicals, originating in the active muscles. in dynamicdynamic exercise, they are carried in the blood to the arterial and medullary chemoreceptorschemoreceptors, and probably have their main effects there in isometricisometric efforts the ventilatory drive originates in chemically sensitive nerve chemically sensitive nerve endingsendings

During the exercise, During the exercise, stimuli stimuli from the muscles, joints from the muscles, joints and perhaps such sensory receptors as pressure and perhaps such sensory receptors as pressure endings in the feet, contribute to the elevation of endings in the feet, contribute to the elevation of ventilationventilation

Recovery and ventilation

Cessation of muscular effort

Normal blood K+ and CO2 oscillations (2-3 min)

Decreased acidity (several minutes)

High temperature

How does the cardiovascular How does the cardiovascular system respond to exercise?system respond to exercise?

Resting Resting cardiac outputcardiac output is typically ~ 5 l/min. is typically ~ 5 l/min.

~ 35 l/min in a well-trained aerobic athlete, and up to 45 l/min in a ultra-elite performers

At VO2max it will be ~ 25 l/min in a healthy but not especially trained young man

Venousreturn

Skin andsplanchnic blood

volume

Maintenance ofventricular fillingMuscle

“pump”

Cardiacoutput

Cardiaccontractility

HR

Dynamic exerciseDynamic exercise ↑ Muscle pump + ↑ symp. vasocon. ↑ Muscle pump + ↑ symp. vasocon. ↑ Venous return ↑ Venous return ↑ ↑ stroke volumestroke volume ↑ ↑ cardiac outputcardiac output

Increased CO can be achieved by raising either stroke volume (SV) or heart rate (HR)steady-state HR rises essentially linearly with work rate over the whole range from rest to VO2max :increased sympathetic and decreased parasympathetic discharge to the cardiac pacemaker + catecholaminesreflex signals from the active muscles blood-borne metabolites from these muscles temperature rise

CCardiac output (CO)ardiac output (CO) increase increase

Heart rateHeart rate

endurance training, especially if maintained over many years, lowers this maximum by up to 15 b.p.m.15 b.p.m.

it also, of course, lowers resting HR

Maximum HR is predicted to within 10 b.p.m., in normal people who are not endurance trained, by the rule:

HR (b.p.m.) = 220 - ageHR (b.p.m.) = 220 - age

Blood Blood PPressure ressure (BP) (BP) also rises in exercisealso rises in exercise

systolic pressure (SBP) goes up to 150-170 mm Hg during dynamic dynamic exerciseexercise;; diastolic scarcely alters

in isometricisometric (heavy static) exercise, SBP may exceed 250 mmHg, and diastolic (DBP) can itself reach 180

Muscle chemoreflexMuscle chemoreflex

Heavy exerciseHeavy exercise ↑ muscle lactate muscle chemorec. and afferent nerves medullary cardiovascular center ↑ sympathetic neural outflow ↑ HR and cardiac output per minute + vasoconstriction (viscera, kidneys, skeletal muscles) + vasodilation in working skeletal muscles

Cardiovascular response Cardiovascular response in in isometricisometric exerciseexercise

Compression of intramuscular arteries and veins prevents muscle vasodilation and increased blood flow↓ oxygen delivery causes rapid accumulation of lactic rapid accumulation of lactic acidacid – stimulation of muscle chemoreceptors – elevation of baroreceptor set point and sympathetic drive (muscle chemoreflexmuscle chemoreflex)As a result: mean BP is higher (as compared with dynamic exercise) systolic and diastolic BP

Strength Strength

trainingtraining

Endurance Endurance

trainingtraining

Chronic Effects of Dynamic ExerciseChronic Effects of Dynamic Exercise(cardiovascular adaptations to dynamic exercise training)(cardiovascular adaptations to dynamic exercise training)

Adaptations that increase muscle oxidative capacity and delay lactate production ↓↓ muscle chemoreflex muscle chemoreflex influence on cardiovascular system

As a result sympathetic activity is decreased, which lowers BP and HR (trained people)

Blood flow Blood flow redistributionredistribution is achieved is achieved partly by sympathetic nerve activity, partly by sympathetic nerve activity,

and partly chemicallyand partly chemically

1400ml/min 1100ml/min 750ml/min 1200ml/min500ml/min250ml/min

300ml/min

1000ml/min

250ml/min 750ml/min 22 000ml/min

Nitric oxide

Exercise

Prostacyclin

ProstacyclinVasodilatorcapacity

Coronary artery

Rest

Coronary artery

Nitric oxide

↑ Cardiac output ↑ Coronary flow (fivefold) ↑ Endothelial cell shear stress ↑ Endothelial-dependent vasodilation + cholinergic fibers stimulation (sympathetic system)

Coronary Coronary blood flowblood flow

How do muscle respond to How do muscle respond to exercise?exercise?

Response to chronicResponse to chronic moderate moderate exerciseexercise

Increased fatigue resistanceIncreased fatigue resistance is mediated by:- ↑ muscle capillary density - ↑ myoglobin content, - ↑ activity of enzymes (oxidative pathways)- ↑ oxidative capacity linked to ↑ numbers of

mitochondria

Increased capacity to oxidize FFAIncreased capacity to oxidize FFA shifts the energy source from glucose to fat (to spare glucose)

Moderate exercise ↑ oxidative capacity and fat usage ↑ VO2max and endurance

↓ lactate

Chronic Effects of Dynamic ExerciseChronic Effects of Dynamic Exercise

Response toResponse to high intensityhigh intensity muscle contractionmuscle contraction

↑ in muscle strength via improvement of motor units recruitment (1-2 weeks of training)

muscle hypertrophy (↑ of muscle contractile elements)

no change in oxidative capacityno change in oxidative capacity

Hormonal responses during Hormonal responses during aerobic exerciseaerobic exercise

Our endocrine system and hormones are key players in managing the body’s chemistry

During exerciseDuring exerciseIf we concentrate on efforts of significant intensity – e.g. 70% VO2max - lasting not less than 30 min, there's a simple rule: all hormones rise over time, except insulinexcept insulin

Norepinephrine rises again ('fight or flight'). Increases glycogen breakdown and elevates free fatty acids; also cardiovascular effects as in anticipatory phase

Glucagon rises (to keep up blood sugar). Increases glucose release from liver

Cortisol rises (response to the stress). Increases use of fatty acids, reinforces glucose elevation

Growth hormone begins to rise (damage repair). Stimulates tissue repair, enhances fat use instead of glucose

Anticipating exerciseAnticipating exercise

Anticipation principally involves the catecholamine hormones, particularly epinephrineepinephrine + + sympathetic sympathetic activationactivation

Systemic effects include: • bronchodilation • intra muscular vasodilatation • visceral and skin vasoconstriction •increased cardiac output

Metabolic effects include: • promotion of glycogenolysis and glycolysis in muscle • release of glucose from liver • release of free fatty acids from adipose tissue.

Cortisol's behaviour is particularly complex. In exercise at low intensity (e.g.30% max - an easy jog) some reports indicate that its level falls (such gentle aerobic exercise relieves stress). When it does rise, at higher intensities, it peaks after 30 min, then falls off again

Other hormones involved in exerciseOther hormones involved in exercise Thyroxine/T3 usually rise somewhat, but less than one might expect. Epinephrine requires more intense effort than norepinephrine to raise it significantly in this phase. 70% max may be barely sufficient. ADH is released in considerable quantities. It's not just socially inconvenient to have to urinate during exercise - it's a waste of fluid which will probably be needed as sweat. Testosterone/estrogen increase with exercise - probably, over many repetitions, promoting increased muscle bulk Aldosterone also rises, reducing Na+ loss in sweat (and in such urine as is still produced).

Insulin concentration falls significantly

after 20-30 min exercise, and goes on

falling (at a lower rate) if the exercise

continues 2-3 hours

Why insulin falls?

How is glucose transport intoHow is glucose transport into skeletal muscle affected by skeletal muscle affected by

exercise?exercise?

How does physical activity affect How does physical activity affect appetite?appetite?

Dailyenergyintake(kcal)

Daily energy expenditure (kcal)

Appetite Appetite ControlControl

↑↑ Energy expenditure Energy expenditure ↓ ↓ bblood glucose + ↑ digestion lood glucose + ↑ digestion rate + ↑ hypothalrate + ↑ hypothalamicamic stimulation stimulation ↑ appetite ↑ appetite

Sport is healthSport is health

True or false?

IIf the type of exercisef the type of exercise

-involves large muscle groups (e.g. cycling, walking, running)

-in continuous activity at an intensity which elevates oxygen consumption/heart rate to an appropriate training level, and

-if this exercise is performed three to five times per week, between 20 and 60 minutes per day,

the aerobic fitness of most people is the aerobic fitness of most people is likely to improvelikely to improve

The choice is yours...The choice is yours...

If the individual becomes sedentary or significantly reduces the amount of training, the effects of training are lost.

The body also adapts to inactivityThe body also adapts to inactivity